Generally, a centrifugal machine is an apparatus for rotating a rotor containing a specimen in high speed, giving the specimen high centrifugal acceleration, so that a specimen of high density is positioned on an outer layer in a radial direction while a specimen of low density is positioned on an inner layer in a radical direction, thereby separating an ingredient thereof
FIG. 1 is a cross-sectional view schematically representing a related centrifugal machine of automatic balance type. As shown in FIG. 1, a related centrifugal machine of automatic balance type is comprised of: a base 2 installed within an outer case 1; a spring 5 installed between a bracket 4 and the base 2 to which a diving motor 3 is mounted, for supporting a rotational part consisting of the diving motor 3 and a rotor, etc. Furthermore, the spring 5 has an indented rubber tube 6 on its outer periphery, so that spring function and attenuation function are provided by means of such spring 5 and rubber tube 6.
In the meantime, a rotor 8 is mounted on an upper portion of a rotational shaft 7 which is supported by a shaft pad in the bracket 4, for free rotation. As a bottom of the rotational shaft 7 is connected to a motor shaft, torque of the driving motor 3 is transferred to the rotor 8. A bucket 9 for accommodating a specimen is mounted on the rotor 8 so that it rotates freely by means of a pin 10. A balancer body 20 of cylindrical shape is fixed on a male screw 11 extended from the rotational shaft 7 in the upper portion of the rotor 8, and a ball 21 is contained within such balancer body 20. In the picture, reference numerals 12, 13, 15 represent a chamber, a chamber door, an unbalance mess, respectively.
The related centrifugal machine of automatic balance type having a constitution as mentioned above, adjusts a ratio of a ball 21 radius to a radius of the cylinder constituting the balancer body 20, distance between a center of the cylinder and a center of rotation, and relation between a concave groove within the cylinder and a half width, thereby correcting unbalance due to a load difference between specimens contained in the bucket 9. More details are described in Japanese Laid-Open Application No. 11-262683 (publication date: Sep. 28, 1999). Accordingly, description thereof is omitted.
According to the foregoing related centrifugal machine of automatic balance type, an unbalance generated from a load difference between specimens that is within a predetermined range can be corrected automatically, but in case of centrifugal machining a specimen beyond such range, a problem that there is no safety device for protecting a specimen and a centrifugal machine. In other words, whenever using a centrifugal machine, a user should determine whether there is a problem in operating the machine before using the machine. If a user does not pay a proper attention like this, an excessive vibration may be generated in a rotational shaft and a specimen is destroyed, and in worst case, a bearing and a driving part including a motor may be broken down, so that life of a centrifugal machine is reduced